Polishing pad and method for manufacturing the same

ABSTRACT

An object of the present invention is to provide a polishing pad capable of obtaining the stabilized polishing performance and a method for manufacturing the same.  
     The polishing pad according to the present invention is characterized in that cut surfaces of not less than one kind of sheets are arranged spirally on the polishing surface of the polishing pad.

BACKGROUND OF THE INVETION

[0001] 1. Field of the Invention

[0002] This invention relates to a polishing pad for accurate polishing for use with a semiconductor wafer, liquid crystal glass, a hard disk and so on, and more particularly to a polishing pad for chem-mechanical polishing used mainly for a process for manufacturing a semiconductor device.

[0003] 2. Description of the Related Art

[0004] With the progress of higher integration and more fitness of a semiconductor integrated circuit, lamination of wiring has been carried out. That is, there is employed a process in which a wiring material is formed in a pattern on the surface of a semiconductor wafer, and is then covered by an insulating film such as silicon oxide or the like, and a next wiring material is formed in a pattern, which process is sequentially repeated.

[0005] When the number of laminations of wiring increases, a difference in level occurs in the insulating film such as silicon oxide or the like, and therefore it is necessary to eliminate a difference in level to flatten before pattern-forming next wiring material, for which purpose, chem.-mechanical polishing is carried out.

[0006] The chem-mechanical polishing comprises polishing a semiconductor wafer to flatten the latter using a polishing pad while supplying polishing liquid (hereinafter referred to as slurry). The high polishing performance excellent in polishing speed or polishing precision is required.

[0007] Particularly, with respect to the polishing precision, it is necessary to fulfill with both flatness of the whole semiconductor wafer surface (hereinafter referred to as global flatness) and flatness of a fine pattern of a semiconductor wafer (hereinafter referred to as local flatness). It is said that these are in a trade-off relation in which when one precision is enhanced, the other is lowered.

[0008] Further, it is necessary to avoid generation of so large flaw (hereinafter referred to as killer scratch) as to influence on the device performance to the utmost.

[0009] The polishing speed, the polishing precision and the generation of killer scratch greatly depend on the properties of a polishing pad in excess of the performance of a polishing device.

[0010] (A) Polishing speed: The holding performance of slurry is good, and an area of a polishing part having micro surface roughness is large.

[0011] (B) Polishing precision: For the global flatness, compressed elastic deformation is large, and for the local flatness, pad hardness is high.

[0012] (C) Pad free from generation of scratch: The surface is of a porous structure, polishing refuse is accumulated on the porous part, and is not present in a polishing part.

[0013] Actual circumstances of conventional pad

[0014] In the conventional polishing pad used, the surface (polishing surface) is of a porous structure from a point of the holding performance of slurry, and the prevention of killer scratch generation. Particularly, a foaming substance having a variety of shapes, density and cell diameters can be manufactured, and a sheet-like pad formed from a polyurethane foaming substance has been widely used for the reason of high abrasion resistance or the like.

[0015] However, when the conventional pad formed of a polyurethane foaming substance is used for a long period of time for polishing, polishing material or polishing refuse becomes clogged up in a hole of closed-cell on the pad surface or the hole becomes compression deformed, thus posing a problem that the polishing performance such as generation of killer scratch or lowering of polishing speed lowers.

[0016] Therefore, it is necessary to carry out dressing for shaving off the pad surface by a diamond cutter or the like every several times of use, and verification of the polishing performance need be carried out every time, which is very inconvenient.

[0017] There is a further problem that unevenness of the cell diameter and density of the foaming substance occurs between the manufacture lots, and unevenness also occurs at a slice part even within the same lot, failing to obtain the stabilized polishing performance.

[0018] There have been proposed a pad in which abrasive grains formed of inorganic particulates are scattered and held in pad material, and the abrasive resistance is adjusted to make execution of dressing unnecessary (self conditioning), and a pad for reducing a using quantity of slurry.

[0019] However, since the above-described pad material is formed of an closed cell foaming substance, it is difficult to manufacture a pad with uniform cell diameter of a foaming substance or density over the whole pad and stably between the manufacture lots, and it is difficult to provide a molded substance with abrasive grains scattered, thus likewise posing a problem that the stabilized polishing performance is not obtained.

SUMMARY OF THE INVENTION

[0020] It is an object of the present invention to provide a polishing pad capable of obtaining the stabilized polishing performance.

[0021] It is a further object of the present invention to provide a polishing pad for making scattered patterns of abrasive grains the same to reduce using quantity of slurry and obtain the stabilized polishing performance.

[0022] It is another object of the present invention to provide a polishing pad capable of reducing peeling between layers even if polishing is done in cut surface.

[0023] It is another object of the present invention to provide a polishing pad without requiring dressing.

[0024] It is still another object of the present invention to provide a method capable of manufacturing a polishing pad industrially easily.

[0025] For achieving the aforementioned objects, the present inventors have studied earnestly and as a result thereof found that if a cut surface of a sheet is used as a polishing surface of a polishing pad, a fine structure of the polishing surface can be made substantially the same, thus obtaining the stabilized polishing performance to accomplish the present invention. However, in prior art, using a cut surface of a sheet as a polishing surface has not at all carried out, and in addition, such an idea has not at all known.

[0026] That is, the present invention is characterized in that not less than one kind of cut surfaces of sheet are arranged spirally in the polishing surface of a polishing pad.

[0027] If the cut surface of a sheet is used as the polishing surface, the same polishing surface is obtained from the same sheet, and even if the polishing surface is shaved off, the inside is also the same polishing surface, and therefore the stabilized polishing performance is obtained.

[0028] When the surface of a sheet is used as the polishing surface, rubbing in a longitudinal direction of fiber occurs resulting in that fiber easily slips out, but when the cut surface is used as the polishing surface, rubbing of an end surface of fiber occurs, and fiber will not slip out even if the fiber is worn out. Therefore, it seems that the stabilized and excellent polishing performance is obtained.

[0029] In the polishing pad according to the present invention, the cut surface of a sheet is disposed spirally. By doing so, even polishing is done by the cut surface, peeling between layers can be lessened. On the other hand, even if the merely laminated cut surface is used as the polishing surface, peeling between layers occurs due to polishing resistance or the like, failing to be used industrially as a polishing pad.

[0030] Further, when at least one kind of the sheet is used as a sheet of abrasive grain, if abrasive grain-contained liquid is applied substantially evenly on the sheet, even if the abrasive grain content of the surface is different from the inside, abrasive grain-contained patterns of the sheet cut surface and the sheet surface, and the inside are substantially the same, and therefore, even if the surface of the pad is shaved off, a substantially constant abrasive grain pattern can be always used as a polishing surface, thus obtaining the stabilized polishing performance.

[0031] Further, the sheet is wound spirally and molded, whereby the polishing pad according to the present invention can be manufactured easily.

[0032] According to the present invention, the thickness dimension of each sheet to be used is selected, and fine structure of a polishing function part resulting from properties of the respective sheet cut surface can be controlled to be constant, thus enabling provision of a stabilized polishing pad free from unevenness of polishing ability.

[0033] The above and other objects and advantages of the invention will become more apparent from the following description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0034] The embodiments of the present invention will be described below.

[0035] The sheet used in the present invention will suffice to be a sheet having mechanical properties capable of being wound spirally, and is not particularly limited. The thickness of the sheet used is approximately 0.05 to 10 mm, preferably, 0.1 to 3 mm. When the thickness of a sheet is less than 0.05 mm, an adhesive between the sheets relatively increases failing to sufficiently function the polishing function of the sheet cut surface; whereas when the thickness exceeds 10 mm, the polishing function of the sheet cut surface is excessively affected so that the polishing ability is controlled by properties of the sheet cut surface, and the sheet cannot be firmly wound spirally and becomes softened, failing to function as a polishing pad.

[0036] As the sheet used in the present invention, chemical synthetic fiber or inorganic fiber processed into a sheet in the form of fabric, non-woven fabric, felt and paper, an elastic high polymer sheet, and a sheet containing an inorganic particulate can be used, but those having a relatively large percentage of void and which are hydrophilic are preferable.

[0037] With respect to the kinds of sheets used in the present invention, one kind will be good, but preferably, a combination of not less than two kinds are used. Particularly, preferably, a sheet containing inorganic particulates and a fibrous sheet may be combined for use.

[0038] As the abrasive grain sheet according to the present invention, those in which abrasive grains are scattered in a synthetic high polymer or those in which abrasive grains are scattered in a binder material and impregnated and filled in a fibrous sheet may be used. After abrasive grain liquid is coated, and for example, a roll is passed through whereby the content of abrasive grains in a sheet can be further made even.

[0039] As abrasive grains used in the present invention, there can be mentioned silicon oxide, cerium oxide, aluminum oxide, manganese dioxide, iron oxide, zinc oxide, silicon carbide boron carbide, synthetic diamond, tourmaline powder, etc., which are used singly or in the form not less than two kinds. As the abrasive grain itself, a known abrasive grain heretofore used the purpose of this kind may be used, and though not particularly limited, the same kind of abrasive grain as the abrasive grain used for slurry at the time of polishing may be used.

[0040] The particle diameter of an abrasive grain used is preferably 0.01 to 10 μm. In a case of this range, they can be scattered with high density and evenly, but when the particle diameter exceeds 10 μm, killer scratch results.

[0041] As a binder for scattering the abrasive grains, there can be suitably used those in which a high polymer such as a polyacrylic series, an epoxy series, a polyurethane series or the like is diluted by water or an organic solvent such as DMF or DEF. The content of abrasive grains in the abrasive grain liquid is preferably, 50 to 90 weight %.

[0042] The polishing pad according to the present invention can be manufactured by winding a sheet cut surface spirally to mold it cylindrically while preferably coating or impregnating a binder in a sheet. The binder may be used merely at the wound end. Further, if the sheet is closely fitted in a cylindrical elastic substance after having been wound, the binder may not be used at all.

[0043] A molded article formed into a cylindrical shape is cut in a direction at right angles to or crossing with a winding axis, and the cut surface is used as a polishing surface to obtain the polishing pad according to the present invention, or a sheet is wound about a shaft while slitting the sheet to a thickness dimension of the polishing pad to obtain the polishing pad according to the present invention.

[0044] As a sheet, if an abrasive grain sheet alone or an abrasive grain sheet and a fibrous sheet are used, a polishing pad using no slurry or reducing a using quantity of slurry can be obtained. Since in this polishing pad, the pad surface is shaved off little by little, dressing need not be carried out.

[0045] According to the polishing pad as described, the polishing performance is imparted by the abrasive grains filled in a pad base, and the pad base has adequate abrasion property, and the surface of the pad is sequentially shaved off little by little according to the number of polishing of wafers to enable polishing by a new surface.

[0046] The reason why when the above polishing pad is used, the stabilized quality of the polishing surface is obtain is that if the abrasive grain-contained liquid is applied generally evenly on the sheet, even if the abrasive grain content of the surface is different from that of the inside, the abrasive grain-contained patterns of the sheet cut surface, and the sheet surface and the inside are substantially the same, because of which polishing can be accomplished always under the constant polishing condition.

[0047] In the past, that abrasive grains are contained in a thin sheet, that the sheet is wound in the form of a roll, and that the cut surface is used as the polishing surface have not been known at all.

[0048] The polishing pad formed by the above-described method is formed in its center with a hole from which a shaft is taken out. The polishing pad can be used without modification depending on the using object, but preferably, the hole is buried with synthetic resin or the like to use as a polishing pad.

[0049] For strengthening binding between the sheets, when the sheet is wound, the sheet may be wound while applying a synthetic high molecular liquid as a binder. As the synthetic high molecular liquid as a binder, there can be used a solvent solution of thermosetting resin of an acrylic series, an epoxy series, a polyester series and a urethane series, or an aqueous emulsion can be used. Further, thermoplastic resin is used, and the sheet may be bound by a heat seal. In sum, in the present invention, the binder is used under the conception including a binder, and if the sheet can be pasted, material is not particularly limited.

[0050] The above-described binder may also have, in addition to the function as binding between sheets, a function as a polishing area by controlling a thickness of coating constant, and a function as a regulating material for elastic compression rate of a pad.

[0051] The present invention will be further explained below referring to Examples, but the present invention is not limited to these examples.

EXAMPLE 1

[0052] Cerium oxide of average grain size 1 μm as abrasive grain was scattered evenly into a methyl methacrylate aqueous solution to prepare an abrasive grain liquid.

[0053] Roll molding was carried out while coating the abrasive grain liquid between two span bond PET non-woven fabrics of width 200 mm and weighing 20 g/m², and the abrasive grain liquid was heated and dried to cure methyl methacrylate and prepare a sheet (A) containing inorganic particulates of thickness 0.3 mm. The weighing of the obtained sheet (A) was 600 g/m² and the content of cerium oxide to the sheet was 79 weight %.

[0054] The sheet (A) containing the inorganic particulates was wound to diameter 200 mm by coating the methyl methacrylate aqueous solution thereon by a transfer roll and pressing it by a touch roll, heating and drying to cure it, then slicing it to prepare a polishing pad of the present invention.

[0055] Surface (polishing surface) hardness of the prepared polishing pad was 96 degrees by an ASKER C-type hardness meter, and density was 2.12 g/cm³.

[0056] A silicon wafer with a film oxide was polished by the obtained polishing pad while supplying slurry having cerium oxide fine powder mixed. Then, polishing speed was 5000 Å/min., and microscratch was not observed on the wafer.

[0057] Further, a silicon wafer with a film oxide was polished by the obtained polishing pad while supplying pure water. Then, polishing speed was 1500 Å/min., and microscratch was not observed on the wafer.

EXAMPLE 2

[0058] The sheet (A) containing the inorganic particulates and span bond PET non-woven fabric of width 200 mm and weighing 80 g/m² were wound to diameter 200 mm by coating the methyl methacrylate aqueous solution thereon by a transfer roll and pressing it by a touch roll, heating and drying to cure it, then slicing it to prepare a polishing pad of the present invention.

[0059] Surface (polishing surface) hardness of the prepared polishing pad was 90 degrees by an ASKER C-type hardness meter, and density was 2.85 g/cm³.

[0060] A silicon wafer with a film oxide was polished by the obtained polishing pad while supplying slurry having cerium oxide fine powder mixed. Then, polishing speed was 3000 Å/min., and microscratch was not observed on the wafer.

EXAMPLE 3

[0061] A sheet (B) of thickness 0.1 mm was prepared by roll molding while coating a methyl methacrylate aqueous solution on span bond PET non-woven fabric of width 200 mm and weighing 20 g/m² heating and drying to cure methyl methacrylate.

[0062] The sheet (B) and span bond PET non-woven fabric of width 200 mm and weighing 80 g/m² were wound to diameter 200 mm by coating the methyl methacrylate aqueous solution thereon by a transfer roll and pressing it by a touch roll, heating and drying to cure it, then slicing it to prepare a polishing pad of the present invention.

[0063] Surface (polishing surface) hardness of the prepared polishing pad was 85 degrees by an ASKER C-type hardness meter, and density was 1.5 g/cm³.

[0064] A silicon wafer with a film oxide was polished by the obtained polishing pad while supplying slurry having cerium oxide fine powder mixed. Then, polishing speed was 2500 Å/min., and microscratch was not observed on the wafer.

EXAMPLE 4

[0065] Cerium oxide of an average grain size 1 μm as abrasive grains was scattered evenly in a water soluble polyurethane emulsion to prepare an abrasive grain liquid.

[0066] The abrasive grain liquid was roll molded while coating it between two span bond PET non-woven fabrics of width 100 mm and weighing 20 g/m², and heating and drying to prepare a sheet (C) containing inorganic particulates of thickness 0.4 mm. Weighing of the obtained sheet (C) was 800 g/m², and the content of cerium oxide to the sheet was 82 weight %.

[0067] The sheet (C) containing inorganic particulates and span bond PET non-woven fabric of width 100 mm and weighing 80 g/m² were wound to the diameter 610 mm in a shaft of diameter 60 mm while coating the water soluble polyurethane emulsion and pressing by a touch roll, and heating and drying to cure it, and thereafter slicing it into a sheet of 2.5 mm thickness, and adhering a urethane sheet of diameter 60 mm and thickness 2.5 mm to a central hole from which a shaft is removed to prepare a polishing pad of the present invention.

[0068] Surface (polishing surface) hardness of the prepared polishing pad was 96 degrees by an ASKER C-type hardness meter, and compression percentage of 1 kgf load was 5%.

[0069] The polishing pad of the present invention is able to control a fine structure of a polishing function part caused by physical properties of a sheet cut surface constant to thereby render a stabilized polishing pad free from unevenness in polishing ability.

[0070] Further, in the polishing pad according to the present invention, since the cut surface of the sheet is made as the polishing surface, the same polishing surface is obtained from the sheet of the same polishing function, and even if the polishing surface is shaved, the inside is also the same polishing surface, and therefore, the stabilized polishing performance is obtained. Further, when the surface of the sheet is made as the polishing surface, it is rubbed in a longitudinal direction of fiber so that the fiber tends to be slipped out. However, since the cut surface is made as the polishing surface, the end of fiber is to be rubbed so that the fiber is not slipped out even if it is worn, thus obtaining the stabilized and excellent polishing performance.

[0071] Furthermore, in the polishing pad of the present invention, the cut surface of the sheet is disposed spirally, and by doing so, even if the cut surface is polished violently, the layers of the sheet are hard to peel off.

[0072] According to the present invention, defects of a conventional sheet-like polishing pad comprising foam polyurethane are overcome to obtain the stabilized polishing performance, and since the surface of the pad is shaved little by little, thus providing an advantage that requires no dressing.

[0073] The entire disclosure of Japanese Patent Application No.223541 filed on Jul. 25, 2000 including specification, claims and summary are incorporated herein by reference in its entirety. 

What is claimed is:
 1. A polishing pad characterized in that cut surface of not less than one kind of sheets are arranged spirally on the polishing surface of a polishing pad.
 2. The polishing pad according to claim 1 wherein a contact part of said sheet is bound though a binder.
 3. The polishing pad according to claim 2 wherein said sheet includes an abrasive grain sheet.
 4. The polishing pad according to claim 3 wherein said sheet is an abrasive grain sheet and a fibrous sheet.
 5. The polishing pad according to claim 4 wherein said abrasive grain sheet is a fibrous sheet of thickness 0.05 to 10 mm containing abrasive grains of grain size 0.01 to 10μ.
 6. The polishing pad according to claim 5 wherein said abrasive grain comprises silicon oxide, cerium oxide, aluminum oxide, manganese dioxide, iron oxide, zinc oxide, silicon carbide, boron carbide, synthetic diamond, tourmaline powder, etc., which are used singly or in the form not less than two kinds.
 7. The polishing pad according to claim 5 wherein said fibrous sheet comprises woven fabric, non-woven fabric or a felt-like fibrous sheet.
 8. The polishing pad according to claim 1 wherein said polishing pad is for chem-mechanical polishing.
 9. A method for manufacturing a polishing pad wherein cut surfaces of not less than one kind of sheets characterized in that a sheet is molded by being wound spirally are arranged spirally on the polishing surface of polishing pad.
 10. The method for manufacturing a polishing pad according to claim 9 wherein the sheet is wound spirally and molded cylindrically while coating or impregnating an adhesive.
 11. The method for manufacturing a polishing pad according to claim 10 wherein a molded article formed into a cylindrical shape is cut at right angles to or in a direction crossing with a winding axis to make a cut surface as a polishing surface.
 12. The method for manufacturing a polishing pad according to claim 11 wherein said sheet is an abrasive grain sheet alone or an abrasive grain sheet and a fibrous sheet. 